Nonon urged me to watch Secret Knowledge by David Hockney on YouTube, and so I did. (I've had the book for several years and my eldest sister Lourdes even ordered of one his modern camera lucidas for me, but I've never actually used it.) Fascinating, and I like Van Eyck's works most of all. Hockney is such a dull commentator, though, and a horrible draftsman. He should have hired other artists to draw and paint over all those projections.